The present invention relates to microelectronic circuit fabrication and structure, and more particularly, to improving the reliability of solid-solder based cooling schemes used in electronic packages.
Solder thermal interface may be used between a processor chip and a heat spreader to effectively remove heat from the processor. Typically, the processor chip is silicon and the heat spreader is Ni-plated copper, an alloy or a composite. However, the relatively rigid solder thermal interface compared to a polymeric TIM or grease, even with the use of softer metals such as indium or its alloys, is prone to cracking in thermal or power cycling due to thermomechanical stresses generated by the coefficient of thermal expansion (CTE) mismatch between the heat-spreader and the silicon chip. The CTE mismatch is exacerbated with a copper heat-spreader which is often used due to cost and thermal conductivity advantages. The dynamic warp of the chip-carrier is another contributor to the propensity for solder TIM cracking and/or thermal degradation in organic, laminate chip-carrier packages. The cracked solder interface results in thermal degradation and an increase in processor operating temperature or a reduction in reliability.
An increase in thermal interface material (TIM) thickness may reduce strain in the TIM and consequently may mitigate the thermal cycling related solder TIM cracking. An increase in TIM bondline may decrease the thermal performance. It is preferable to use a thinner bondline to obtain good thermal performance. Also, due to the dynamic warp associated with laminate chip-carriers, organic packages with solder thermal interface are susceptible to TIM cracking and associated thermal performance deterioration in the field. The proclivity for solder cracking may increase as the die size increases.
A liquid metal TIM may be used to benefit from the higher thermal conductivity of a metal TIM, while eliminating the fatigue cracking related degradation of a solid metal TIM (solder). Liquid metal cooling schemes may benefit from the high thermal conductivity of liquid metal alloys. However, the liquid metal cooling requires containment schemes to prevent the material from leaving the interface and shorting exposed components adjacent to the die or on the board. Oxidation and corrosion barriers may be required to protect the liquid metal TIM from degrading and impacting thermal performance or reliability.
For applications involving large chips, high chip-powers, multi-core chips with non-uniform power distribution and hot spots, or devices requiring more power cycles to accommodate power management applications, a high thermal performance, reliable thermal interface solution is needed.